This research was undertaken to clarify effects of thermal aging on electrochemical and mechanical properties of superaustenitic stainless steel and to detect the material degradation nondestructively. The steel was artificially aged at $300{sim}650^{circ}C$ for $240{sim}10,000h$ and the mechanical properties were investigated at $-196{sim}650^{circ}C$ using small punch(SP) test. Also, the change in electrochemical properties caused by effects of thermal aging on superaustenitic stainless steel was investigated using electrochemical anodic polarization test in a KOH electrolyte. Carbides and ${eta}-phase(Fe_2Mo)$ precipitated in the grain boundaries seem to deteriorate the mechanical properties by decreasing cohesive strength in the grain boundaries and to promote the current density observed in electrochemical polarization curves, The electrochemical and mechanical properties of superaustenitic stainless steel decreased significantly in the specimen aged at $650^{circ}C$ corresponding to the sensitization temperature for conventional austenitic stainless steels.